Would it be possible to include the following on TreeCache:
boolean exists(Fqn fqn, String key)
I recently added an exists(Fqn) method, I'll add another one for exists(Fqn, Object key).
Note, that there is a diff between get() and exists(): get will try to load the node/value from the CacheLoader, whereas exists() will not (just a memory check).
Bela